The quest for alternative fuels, including natural gas, will result in compressed natural gas cylinders being found in cars and trucks with increasing frequency. Federally mandated regulations set forth various applicable safety standards. Those standards require that compressed natural gas containers include relief valving mechanisms which allow gaseous contents under pressure to escape from the container before reaching an unacceptably high pressure. Absent such relief mechanisms, the gaseous contents may become explosive, since the pressure of a fixed mass of gas is directly proportional to its temperature.
One approach to designing safety gas containers is disclosed in U.S. Pat. No. 4,660,7I4 which issued on Apr. 28, 1987. The '714 patent is incorporated herein by reference. It discloses the use of a valve member made of a shape memory alloy which is previously made to remember a smaller shape at a specific (high) transformation temperature. As the shape memory valve member is diminished in size in response to a rise in ambient temperature above the transformation temperature, a gap occurs between the valve member and the gas passageway, so the gas may escape before its pressure becomes unacceptably high. The '714 reference however is suitable only for low pressure applications, and is not well adapted to applications wherein pressures amounting to about 5,000 psi are exerted. This is because high internal pressures will keep the disclosed valve member seated and will not allow gas to escape. Additionally, the '714 disclosure contemplates allowing gas to escape at a small rate so as to avoid propelling the container.
Against this background, the need has arisen for a compressed gas container which serves as a safe reservoir that allows gas to escape whenever internal pressures rise above an unacceptable level.
Additionally, it would be desirable to take advantage of the unique thermo-mechanical properties of shape memory alloys which can be used as a suitable valving mechanism.